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11.
A late Pliocene diatom Ge/Si record from the Southeast Atlantic 总被引:1,自引:0,他引:1
As a result of both culture and sediment core studies, the ratio of germanium (Ge) to silicon (Si) in diatom shells has been proposed as a proxy for monitoring whole-ocean changes in seawater Ge/Si, a ratio affected by changes in continental weathering. However, because of the difficulties of extracting and cleaning diatom frustules from deep-sea sediments, only samples from highly pure diatom oozes in the Antarctic region have been previously analyzed. Here we present data on diatom Ge/Si ratios, (Ge/Si)opal, for the time interval between 3.1 and 1.9 Ma from a mid-latitude, coastal upwelling area where significant terrigenous sediment input complicated the sample processing and analyses. In general, our (Ge/Si)opal values show the same decreasing trend after 2.6 Ma than previously measured in Antarctic sediments (Shemesh et al., 1989. Paleoceanography 4, 221–231), but with a noisier background that may reflect the local imprint of proximal continental input superimposed upon global changes in the ocean reservoir. The time of initiation of large-scale North Hemisphere glaciation at 2.6 Ma is characterized by a declining pattern of diatom Ge/Si ratios, which could have resulted from a global increase in the input of riverine Si due to enhanced silica weathering and/or equatorward (northward) intrusions of subantarctic waters enriched in silica. High (Ge/Si)opal ratios are associated with high opal contents from the same sediment samples and with warm climate as indicated by depleted benthic foraminiferal δ18O values from the North and Equatorial Atlantic. Cold periods signified by enriched benthic δ18O values, on the contrary, are associated with lower (Ge/Si)opal ratios. We interpret diatom Ge/Si values to reflect the prevailing weathering state on the continents, with greater chemical weathering during warm and wet periods of the Pliocene and less during cooler and drier intervals. 相似文献
12.
13.
Kazuo Abe 《Journal of Oceanography》2008,64(6):961-967
From August 2006 to August 2007, the concentrations of dissolved silica (Si(OH)4) were monitored in the surface water of Urasoko Bay and the mouth of the stream that runs into the bay. Urasoko Bay is located
on the northern coast of Ishigaki Island, Okinawa, Japan, which is in a subtropical area of the North Pacific Ocean and is
surrounded by a relatively poorly developed fringing reef. Added to these samples were freshwater from the upstream area and
brackish water that exudes at the beach site, which were collected from April to June 2007. Rainwater samples were also collected
during the study period. The concentration of Si(OH)4 generally decreased from upstream to the bay site, and, on clear days, Si(OH)4 data from all study sites (the bay, beach, stream mouth, and upstream) plotted against salinity fell on a single straight
line. When the influence of rainwater was, the results were scattered below the straight line, which suggests dilution by
rainwater with a much lower Si(OH)4 concentration. These findings show that offshore seawater, rainwater, and upstream freshwater regulate the concentration
of Si(OH)4 in the surface water of Urasoko Bay. 相似文献
14.
石榴石-黑云母地质温度计在四川拉拉铜矿床的应用 总被引:7,自引:0,他引:7
在晋宁运动中,拉拉铜矿床区发生了大规模的区域变质作用,由于其变质条件的资料较少,使得人们对矿床的成因机制存在诸多争论.采用石榴石-黑云母地质温度计和多硅白云母地质压力计,结合电子探针分析结果,对矿区内广泛出露的石榴石黑云母片岩进行了研究,得到区域变质作用的变质温度为500~560 ℃,变质压力上限为0.6~0.73GPa,变质程度为高绿片岩相.同时,根据野外观测及室内研究并结合前人工作,认为矿床主要存在两个成矿期次,即火山-喷气沉积成矿期和变质热液成矿期. 相似文献
15.
16.
仇山酸化钙基膨润土的 27Al和 29Si 魔角旋转核磁共振谱及脱色率研究 总被引:1,自引:0,他引:1
对用不同酸度处理的仇山钙基膨润土进行了化学分析、X射线衍线(XRD)、^27Al和^29Si魔角旋转核磁共振(MAS NMR)、吡啶吸附样品的红外光谱(IR)、比表面积、阳离子交换容量(CEC)和脱色率等测定。结果表明,随着处理酸度的增加和蒙脱石中阳离子的溶出,它的d(001)的衍射强度降低,同时其Si和Al原子局域结构环境发生了显著的改变,Al原子由Al^Ⅵ变成Al^Ⅵ,Si原子由Q^Si(0Al)结构向Q^4Si(0Al)和Q^3Si(1OH)结构转变。八面体片阳离子的溶出和Si,Al原子局域结构环境的转变,显著地增加了比表面积和孔结构;Al^Ⅵ向Al^Ⅵ的转变形成了Lewis酸中心,而Si原子局域结构环境的改变形成了Br φnsted酸中心。膨润土脱色率随处理酸度增加的本质原因是在Si和Al原子局域环境的变化过程中,在其表面分别形成了Brφnsted酸中心和Lewis酸中心。 相似文献
17.
地质流体自然类型与成矿流体类型 总被引:16,自引:2,他引:16
水是地球上特征的地质流体 ,大部分矿床是在水热流体参与下形成的 ,但并不是所有流体都参与成矿。根据水的主要存在环境把水分为地质流体和成矿流体类型。各种环境广泛存在的水所构成的地质流体 ,又可细分为大气降水、盆地建造水、海水、岩浆水和变质水各种类型。研究认为成矿流体的形成主要与地质作用有关 ,是地质流体在特定环境特定演化阶段形成的特征产物。成矿流体则可划分为高温硅钾卤水、中温碳酸盐卤水及低温硫酸盐卤水。高温硅钾卤水中硅钾组分含量与温度、盐度成正相关关系 ,并且其中富含F-、B2 O3组分。这些特征与成矿作用中的高温钾化、硅化、萤石化及电气石化蚀变及热水沉积特征是一致的 ,高温成矿流体在演化过程中依次可以演变为中温或低温成矿流体。中温成矿流体以碳酸盐型流体为主 ,以富含Mn2 +,Fe2 +,Mg2 +的碳酸盐化合物为特征。低温成矿流体一般为硫酸盐型卤水 ,主要是Ba2 +,Sr2 +,Ca2 +的硫酸盐化合物 ,在海陆相各环境中广泛存在。大洋底部成矿流体是特殊环境下的地质流体类型 ,具有更广泛的温度区间 ,可以是从高温到中低温的系列流体类型 ,并且具有特殊地球化学组成。一般形成高温硅钾卤水与岩浆作用或变质作用有关 ,由于充分的水岩交代作用 ,可以获得较高的温度及足够的溶质组分 ; 相似文献
18.
Y. Kudoh 《Physics and Chemistry of Minerals》2001,28(8):523-530
The sequential displacement mechanism based on the oxygen-lattice cubic closest packing (c.c.p.) in the < 2 0 1 > direction was proposed in this study. All displacements of cations are within the OT and the O layers with the length of displacement vector being around 1.7 or 2.9 Å, contrary to displacement of around 5.0 Å for models proposed previously. The difference in atomic arrangement between hydrous wadsleyite and hydrous ringwoodite is small. The atomic arrangement of the O layer of hydrous wadsleyite is essentially the same as that of hydrous ringwoodite when Mg vacancies preferentially exist in the O layer. The partial occupancies of normally vacant tetrahedral sites reported in the hydrous-β and hydrous-γ structures may possibly be caused by the existence of Mg vacancies at the octahedral sites through phase transition from hydrous-β to hydrous-γ or from hydrous-γ to hydrous-β phases. 相似文献
19.
J. A. Kamalakar K. V. S. Bhaskar A. S. Laxmi Prasad R. Ranjith K. A. Lohar R Venketeswaran T. K. Alex 《Journal of Earth System Science》2005,114(6):725-731
Lunar Laser Ranging Instrument (LLRI) proposed for the first Indian lunar mission Chandrayaan-1 is aimed to study the topography
of the Moon’s surface and its gravitational field by precisely measuring the altitude from a polar orbit around the Moon.
Altimetry data close to the poles of the Moon would also be available from the instrument, which was not covered by earlier
missions. This instrument supplements the terrain mapping camera and hyperspectral imager payloads on Chandrayaan-1. The instrument
consists of a diode pumped Nd:YAG pulsed laser transmitter having 10 nsec pulse width and a receiver system. The receiver
system features 17 cm diameter Ritchey—Chrétien collecting optics, Si Avalanche Photo Detector (APD), preamplifiers, constant
fraction discriminators, time-of-flight measurement unit and spacecraft interface. Altimeter resolution of better than 5 m
is targeted. The received signal strength of LLRI depends on laser pulse backscatter from the Moon’s surface. Moon’s surface
being a poor reflector, the choice of receiver size and its type and the selection of detector play an important role in getting
a good signal-to-noise ratio and in turn achieving the target resolution. At the same time, the spacecraft puts a limitation
on payload size and weight. This paper discusses the proposed LLRI system for Chandrayaan-1 and signal-to-noise ratio estimation. 相似文献
20.
The main driving force behind Al/Si ordering in tetrahedral framework aluminosilicates is nearest-neighbour Al/Al avoidance.
Computer simulation is used to explore the direct consequences of such Al/Al avoidance. The main result is that the order-disorder
transition temperature T
c
falls dramatically as the concentration x of Al in the structure is reduced, and if the only interactions are those associated with nearest-neighbour Al/Al avoidance,
T
c
becomes zero for x less than some critical value x
c
, where x
c
=0.31 for the feldspar framework and x
c
=0.34 for cordierite. Also a large degree of short range order is found above T
c
. Both results differ radically from the standard Bragg-Williams model. Plots of entropy and enthalpy of ordering are given
as functions of x and T, which may be used to interpret experimental data or for extrapolation into ranges of x and T inaccessible to experiment.
Received: 14 May 1997 / Revised, accepted: 2 June 1997 相似文献